FIG. 1 represents an example of a communication system in which a mobile carrier P, for example an aircraft, communicates with a network of fixed infrastructure R. Such a system is for example adapted to implement the ATN (Aeronautical Telecommunication Network) standard specified by the International Civil Aviation Organization (ICAO).
The mobile carrier P comprises at least one onboard embedded radio communications equipment item 101 which enables it to be connected to an onboard local area network 102.
The mobile carrier P connects to the fixed infrastructure network R through an access gateway 103, 104, 105. This gateway establishes a radio link with the airborne communications equipment item 101 according to a radio communication technology, for example a satellite communication link. The mobile carrier P connects to an access gateway 103, 104, 105 which is within its radio range. Thus, the access to the network R can be made via different access gateways 103, 104, 105. Each access gateway is connected to a home agent 106, 107, which is an entity of the network R whose role is to manage the mobility of the equipment items that want to connect to the network via the access gateways. Each radio communications equipment item 101 is associated with a home agent 106, 107. A home agent 106 can be implemented in an equipment item distinct from the access gateway 103 while being linked to this gateway or be implemented in the same equipment item as the access gateway 103. One and the same home agent 106 can be linked to a plurality of access gateways 103, 104, 105.
In the example of FIG. 1, a communication link between the embedded equipment item 101 and a remote terminal 108 connected to the network R is considered by way of illustration. The mobile carrier P moves from a first zone within radio range of a first gateway 105 to a second zone within radio range of a second gateway 103.
To establish and maintain the communication between the embedded equipment item 101 and the remote terminal 108 regardless of the position of the mobile carrier P, two network links are established.
A first network link is established between the embedded equipment item 101 and the remote terminal 108. The link is established from a permanent network address of the embedded equipment item 101 and a permanent network address of the remote terminal 108.
In order to manage the mobility of the carrier P, a second network link is established in tunnel mode between a temporary network address of the embedded equipment item 101, which belongs to the same network as the access gateway, and the network address of the home agent 106 responsible for the mobility management. The temporary network address is allocated by the network access gateway.
This mobility management mechanism makes it possible to avoid the implementation of complex routing mechanisms when the carrier P changes access gateway during its movement.
However, the use of two network links, including one through a tunnel, for the same point-to-point communication, leads to drawbacks. A transmitted data packet comprises two network headers of significant size, in particular for networks that use the IPv6 protocol. An IPv6 header has a size of 40 octets. Now, the radio link between the mobile carrier P and the network access gateway is more often than not a link with low available bandwidth, in particular for the case of an aeronautical communication link. The use of two IPv6 headers to establish a communication link leads to a non-optimal use of the resources available on the radio channel because the introduction of two network headers in each transmitted packet accordingly reduces the bandwidth available for the useful data transmitted.
One known solution which makes it possible to optimize the radio resources in the case of transmissions based on the IP network protocol consists in using a network header compression mechanism, such as the RoHC (Robust Header Compression) mechanism standardized by the IETF organization under the reference RFC3095.
This mechanism makes it possible to reduce the size of the network header but does present other drawbacks. It requires an initial phase of preliminary connection of the hosts for each interchange session and is complex to implement. Furthermore, it also requires the synchronization to be maintained between the contexts saved by each host to be able to correctly operate the decompression of the headers and is therefore sensitive to any desynchronization phenomenon.